More than 170 people were killed in the crash, and since many of them were Swedes, a representative of the Swedish Accident Investigation Board will formally participate in an investigation into why the plane crashed.

- It is the Iranian security authority that is leading the investigation, ours and my role are very peripheral. We have reached out and offered our help to the Iranian authority and they have kindly thanked for it, says Peter Swaffer.

He believes that the plane's travel registrar, often called the black box, may be able to clarify what happened to the plane.

- It records thousands of parameters about what the aircraft has in store: how the rudders are, the engines, pressure temperatures and everything. Once you have downloaded that data, it will speak its clear language of what has happened. If, for example, it has ceased to record information, then it is obviously something that could prove that something very dramatic has happened, says Peter Swaffer.

"Everyone stretches out a hand"

That the US-made plan has crashed in troubled circumstances will play a part in the investigation, he says, but adds:

- My experience is that the society within the security leading authorities is very good, you help each other, it is very open, everyone is there for each other. And I notice now that everyone stretches out one hand. Then you do not know what other interests there are, if there are political governments in the country higher up, if they tighten muscles.

Peter Swaffer thinks it will be difficult for Iran to withhold what actually happened to the planet.

- As far as I understand, help from other countries has been requested to download the information from the travel registrars, if it becomes the UK or Canada we will see. It doesn't make it any easier if you want to hide something.